1. Field of the Invention
This invention relates to a method for electrically connecting conductors and electrodes in an implantable lead.
2. Description of the Prior Art
A lead for biomedical stimulation generally includes a lead body and one or more exposed electrodes for making electrical contact with body tissues. The lead body essentially includes one or more conductors electrically connected to the electrodes, and one or more insulating materials enclosing the conductors and also forming a lead casing. Generally, the casing is made of a flexible, body compatible material such as silicon rubber or the like. Between each electrode and the lead body there is a juncture, which is critical to the proper functioning of the lead. The juncture must withstand body fluid penetration and ensure the electrical connection between the electrode and the related conductor.
There are various known methods of making such electrical connections.
U.S. Pat. No. 4,381,014 teaches simultaneous connecting and sealing of a juncture by welding an axially extending supplementary wire to several turns of a single-pole, helix-formed conductor at predetermined electrode locations before the conductor is encased in the insulating sheath. Subsequently, the electrode is swaged to cause the wire to penetrate the insulating sheath and establish electrical connection of the conductor and the electrode. Simultaneously, the crimped (swaged) electrode seals the juncture at the ends of the electrode.
An example of a connection in a bi-polar lead is given to U.S. Pat. No. 3,769,984. The lead disclosed therein has two parallel, longitudinally extending non-helical wire conductors in an extruded lead body. The conductors are connected to a pair of axially separated electrodes at the lead distal end. The axial separation between the electrodes corresponds to the axial separation between the distal ends of the conductors, which ends are brought out from the lead body through bores and then connected to the electrodes by, for example, being clamped between a crimp ring and the electrode.
In these examples, with one or two conductors in the lead body, conductor selection at a desired electrode location does not pose a problem with respect to the connection method. In contrast, modern tubing leads, as disclosed, for example, in U.S. Pat. No. 4,484,586, require the electrodes to be attached to a tubing lead body structure comprising several, individually insulated, helically wound conductors. The axial separation between the turns of different conductors in the helix is very small, for example, about 0.2 mm. From this bundle, the conductor to be connected to a certain electrode should be quickly and reliably selected, made free from insulation and adapted for connection at a desired electrode location.